High frequency inductor for small diameter holes



Oct. 15, 1957 H. A. MESSNER 2,81

HIGH FREQUENCY INDUCTOR FOR SMALL DIAMETER HOLES Filed Sept. 26, 1955 INVENTOR. HARLAN A. MESSNER /1 I ORN United States Patent HIGH FREQUENCY INDUCTOR FGR SMALL DIAMETER HOLES Harlan A. Messner, San Marino, Califl, assignor to The Ohio Crankshaft Company, Cleveland, Ohio Application September 26, 1955, Serial No. 536,439

2 Claims. (Cl. 219-1051) This invention pertains to the art of high frequency induction heating and more particularly to an inductor for heating the surfaces of small diameter holes.

In the art of high frequency induction heating, dithculty has always been experienced in heating small diameter holes or openings. Heretofore it has been conventional to position an inductor in the hole having an external surface and current path concentric with the hole surface. As the hole gets smaller and smaller, however, the dimensions of the conductor forming the inductor becomes very appreciable in relation to the hole size and the heating becomes more and more difficult. Eventually a dimension is reached wherein no heating can be accomplished.

The present invention contemplates a high frequency inductor which overcomes these difliculties and successfully heats small diameter holes for various heat treating purposes.

In accordance with the invention, there is provided a high frequency inductor for heating the surfaces of holes, openings or bores in metallic workpieces comprising a pair of parallel extending spaced conductor legs, the remote surfaces of which are workpiece facing surfaces, and magnetically permeable material of a generally circular cross-section and diameter generally equal to the spacing of said surfaces, disposed between and encompassing the surfaces of the legs other than the workpiece facing surfaces. Means are provided for relatively rotating such inductor and the workpiece about the axis of the hole when the inductor is disposed in such hole.

The magnetically permeable material may be either of the powdered or laminated type. In the latter event, each lamination is generally in the shape of a semicircle with each semicircle being associated with one of the legs, and opposed semicircles being electrically insulated from each other.

The principal object of the invention is the provision of a new and improved high frequency inductor which will readily and efliciently heat small diameter holes, openings or bores.

Another object of the invention is the provision of a new and improved high frequency inductor comprised of a pair of parallel extending legs and magnetically permeable material disposed between the legs which will assist in the heating operation.

The invention may take physical form in a number of ditferent appearing parts and arrangements of parts, a preferred embodiment of which will be described in this specification and illustrated in the accompanying drawing which is a part hereof and wherein:

Figure l is a side elevational view, partly in sections, of a high frequency inductor embodying the present invention in operative relationship in the hole of a workpiece.

Figure 2 is a cross-sectional view of Figure 1 taken approximately in the line 2-2 thereof.

Figure 3 is a top elevational view of a lamination employed in the preferred embodiment.

Referring now to the drawing wherein the showings are for the purposes of illustrating the invention only and not for the purposes of limiting same, Figure 1 shows a metallic workpiece A of substantial thickness having a hole It), the surfaces 11 of which are to be heated.

Disposed within the hole 10 is a high frequency inductor B connected through suitable rotating contacts C to a high frequency power source shown schematically at D.

The inductor B is comprised of a hairpin shaped conductor including a pair of spaced parallel extending legs 14 of electrically conductive material electrically connected, at the lower ends by a. base 15. As shown, the conductors 14 and 15 have a hollow interior 16 through which a cooling medium such as'water or the like may be flowed as is conventionalin the high frequency induction heating art.

The legs 14 have remote surfaces 18 which form the workpiece facing surfaces of the inductor B. As shown, the legs 14, 15 are so spaced as to position the surfaces 18 in close spaced relationship with the surfaces 11 of the hole 10. The closer the spacing, the greater the electrical coupling to the workpiece A but such spacing must be limited in relation to the necessity that the indicator B should not touch the workpiece A during a heating operation, and this is so particularly in view of the fact that the inductor B will be rotated within the hole 10 during the heating operation.

The legs 14 and 15 may be of any desired electrically conductive material, copper being preferred.

Magnetically permeable material indicated generally at E is disposed between the legs 14 and has a generally circular cross-sectional shape such as to substantially fill the opening 10 and to partially surround the surfaces 19 of the legs 14 other than the workpiece facing surfaces 18.

The magnetically permeable material may generally be of any desired magnetically permeable material but, as between the two legs 14, must present either a high degree of electrical resistance or other means must be provided to provide electrical insulation between the two legs 14.

The magnetically permeable material E in the preferred embodiment of the invention is comprised of a pair of stacks 25 of thin magnetic laminations 20, each stack having a generally semi-circular cross section substantially as is shown in Figure 3. Centrally of the curved outer surface, a circular notch 22 is provided through which the legs 14 extend. It will be noted that in effect the magnetically permeable material surrounds the sur faces 19 of the legs 14 and is in close contact therewith.

The outer diameter of the laminations 20 is such as to substantially fill the diameter of the opening 10 while allowing suflicient mechanical clearance to permit rotation of the inductor B during a heating operation.

A sheet of electrical insulation 27 is positioned between the two stacks of the laminations. This sheet 27 should be kept as thin as possible so that the maximum amount of magnetic material may be disposed between the legs 14. The laminations 20 are each made of as thin a magnetic material as is available and each lamination should be suitably varnished before assembling into the stack shown, to provide electrical insulation between laminations and reduce eddy currents.

At the end of the stack of laminations 20 is a similarly shaped lamination 30 of copper which is braized to the the legs 14. The copper lamination 30 serves to hold the magnetic laminations 20 in assembled relationship, and also to assist in cooling the lamination by conducting heat generated in the laminations to the water cooled legs 14.

It willbe noted that the axial'length of the magnetically permeable material E is somewhat greater than the axial length of the hole 10, that is to say, the thickness of the workpiece A.

In operation, 'the'indu'ctor B is positioned within'the hole was shown in Figure 1. The inductor'is rotatedby anysuitable meansnot shown'an'd'at any desired rotational speed. High frequency currents are fed to the inductor from the power source 'Dthrough the rotatable contactC. 'These high frequency currentscrea'te a magnetic flux field which induces high frequency currents to flow in'the'surface 11 of the hole '10. These high frequency currents cause the surface 11 of the hole 10 to rapidly heat. When the heating operation "has been completed, surfaces 'of 'thehole 11 may :be quenched 'if desired or allowed to cool slowly, depending "upon the characteristics desired for the "surface of the hole 10. The inductor "B may be removed eitherbefore, during, or after "this subsequent cooling "treatment.

The present inductor has "proven extremely'satisfa'c'tory in heating small diameter holes in relativelylongdiameter openings which could not otherwise be heatedby any known high frequency inducing coils. It thasproven'extremely practicable and durablein practiceandrelatively efficient electrically.

It will be appreciated that modifications and alterations of the invention Will'occur'to othersup'on area'ding and understanding of this specification, audit 'is my intention to include all such modifications and alterations insofar as they come within the scope of the appended claims.

Having thus described my invention, I claim:

1. A high frequency inductor 'foruse inheating'small diameter holes in metallic workpieces comprising in combination aU-shaped-conductor having a pair'of spaced parallel extending legs, the outer or remote surfaces of which form workpiece facing surfaces and are spaced to a distance approximately the diameter of the hole to be heated, said conductor having a portion electrically interconnecting the ends of said legs into a series circuit therewith, and a stack of magnetically permeable laminations having their plane perpendicular "to the length of said le s and spaced fromsaid'p'o'rtion and disposed between said legs, and means electrically'insulating one leg from the other.

2. A high frequency inductor for use in heating small diameter holes inm'etallic workpieces comprising in combination a hairpin shaped conductor .having a pair of spaced parallel extending legs, said conductor having a portion electrically interconnecting the ends of said legs, a stack of laminations of a diameter approximating the diameter of the hole to be heated, comprised of two semi-circular stacks 'one positioned along each leg and spaced from saidportion with a 'layero'f electrical insulationtherebetween, saidlaminations having their plane perpendicular-to the length of said legs, each stack having anotch along its outer'edge to receive'its respective leg.

References Cited in the file of this patent UNITED STATES PATENTS 1,912,214 INorthrup May 30, 1933 2,472,445 Sprong June 7, 1949 2,493,950 Dow et al. Jan. 10, 1950 2,599,086 Beckius et a1. June 3, 1952 2,655,589 Sorensen Oct. 13, 1953 

